Swell is a 14-HP vacuum tube signal processor for Eurorack

4-pole LPF built around a Soviet military-spec subminiature valve, with CV-controlled filter cutoff and resonance, and full control over how the valve operates in the signal path.

At its core, Swell is a 14-HP voltage-controlled 4-pole low pass filter (LPF). But where it diverges from every other filter in your rack is what sits in the signal path: a Soviet military-spec subminiature vacuum tube, originally designed for MiG fighter avionics and early orbital satellites. This isn't nostalgia or gimmickry—it's a deliberate marriage of vintage valve technology and modern synthesis architecture, engineered to give you a sonic palette that no solid-state circuit can replicate.

The valve doesn't just "colour" your sound. It actively reshapes it, generating harmonics, compressing dynamics, and folding waveforms in ways that evolve with every voltage change, every envelope, every modulation source you patch. And because Swell gives you unprecedented control over how the valve operates—switching between triode and pentode modes, shifting bias from clean to heavily saturated, and placing the valve before or after the filter—you're not locked into a single "tube sound."

You have access to a continuum: from transparent filtering with subtle warmth, through classic tube overdrive, all the way to extreme asymmetric wave-folding that turns simple waveforms into complex, evolving textures.

The low-noise 4-pole filter (24 dB/Oct) provides 1V/Oct tracking, temperature compensation, a unique character under resonance and the ability to compensate for output loss gain as well as different timbre with and without compensation.

The addition of audio frequency modulation with a dedicated attenuverter control enables the filter to enter into the uncharted territories by applying different levels of feedback into the filter frequency control.

This is a filter that responds. That breathes. That feels alive under your hands.